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Bell's Palsy

Summary

  • Acute, unilateral facial nerve paralysis of unknown etiology
  • Characterised by sudden onset of facial weakness, typically affecting one side of the face
  • Diagnosis primarily clinical, with imaging used to rule out other causes

Pathophysiology

  • Exact cause unknown, but believed to involve inflammation of the facial nerve (CN VII)
  • Possible triggers include:
    • Viral infections (e.g., herpes simplex virus, varicella-zoster virus)
    • Immune-mediated processes
    • Vascular ischaemia
  • Inflammation leads to compression and oedema of the facial nerve within the facial canal

Demographics

  • Annual incidence: 15-30 cases per 100,000 population
  • Affects all age groups, but peak incidence in 15-45 years
  • Slightly higher prevalence in:
    • Pregnant women
    • Patients with diabetes mellitus
    • Individuals with upper respiratory tract infections

Diagnosis

  • Primarily clinical, based on:
    • Sudden onset of unilateral facial weakness
    • Inability to close eye or wrinkle forehead on affected side
    • Drooping of corner of mouth
  • Physical examination:
    • House-Brackmann scale to grade facial nerve function
    • Assessment of taste and lacrimation
  • Exclusion of other causes (e.g., stroke, tumour) through history and examination

Imaging

  • Not routinely required for diagnosis
  • May be used to rule out other causes or in cases of atypical presentation
  • Modalities:
    • MRI:
    • T1-weighted with gadolinium: enhancement of the facial nerve
    • FLAIR: hyperintensity of the facial nerve
    • CT:
    • Limited role in acute setting
    • May show bony erosion in chronic cases
  • Findings:
    • Enhancement and swelling of the facial nerve, particularly in the labyrinthine and tympanic segments
    • Normal brain parenchyma

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  • 50-year-old patient presented with right sided facial weakness affecting the forehead.
  • MRI showed a FLAIR hyperintensity, mild thickening, and pathological enhancement (labyrinthine, tympanic and mastoid segments; red arrow) of the right facial nerve and a normal left facial nerve (blue arrow).

Treatment

  • Supportive care and medical management:
    • Corticosteroids: Prednisone 60-80 mg daily for 5-7 days
    • Antiviral therapy (e.g., valacyclovir) in combination with corticosteroids
  • Eye care:
    • Artificial tears and eye ointment
    • Taping eyelid closed at night
  • Physical therapy:
    • Facial exercises to maintain muscle tone
  • Surgical decompression:
    • Reserved for severe cases or those with poor recovery
    • Controversial and not routinely recommended
  • Prognosis:
    • 70-80% of patients recover completely within 3-6 months
    • Poor prognostic factors: complete paralysis, age >60 years, hypertension, diabetes

Differential diagnosis

Differential Diagnosis Distinguishing Feature
Stroke Typically affects lower face only; other neurological deficits often present
Ramsay Hunt syndrome Presence of vesicles in ear canal or on palate; severe otalgia
Vestibular schwannoma Gradual onset; hearing loss; tinnitus; balance problems
Parotid gland tumour Slow, progressive facial weakness; visible or palpable mass
Facial nerve trauma History of facial injury or surgery
Melkersson-Rosenthal syndrome Recurrent facial palsy; lip swelling; fissured tongue